Fig. 7. (A) The effect of external Cu (Cu_o) on the Na⁺ content of intestinal cells in the presence of normal (140 mmol l^–1, open bars) and low (11 mmol l^–1, black bars) external Na⁺ (Na⁺_o) after a 15 min incubation in Cu-containing saline at room temperature. (B) Na⁺ content of intestinal cells incubated at the same Cu_o range but at 4°C and with normal Na⁺_o throughout. Values are means ± S.E.M. of N=5–6 separate experiments using fresh cells from different individual fish. ^*Significantly different from control with no added Cu within treatment by Kruskal–Wallis test (P <0.05). No differences were observed in cell Na⁺ content between low and normal Na⁺_o within each Cu_o at room temperature (Student's t-tests, P>0.05). Note the larger y-axis scale in B, all values at 4°C were significantly different from the respective room temperature control within Cu_o treatment (comparison of normal NaCl in A with B, Student's t-tests, P>0.05; data not labelled for clarity). There were no differences between Cu_o-free (EDTA, no added Cu but + 1 µmol l^–1 EDTA) and controls with no added Cu within treatments (Student's t-test, P>0.05).